1. Field of the Invention
The invention relates to load bearing support posts generally and more specifically to yieldable mine posts used as permanent primary supports or secondary rehabilitative supports in subterranean cavities. It is applicable and effective for use with any load support application where there are heavy forces involved and the two surfaces being supported may shift relative to one another.
2. Description of the Current State of the Art
In the field of mining, material is removed to form a variety of subterranean cavities. The weight of the material above the cavity has a tendency to settle into the cavity making necessary the use of various types of support props to resist this settling tendency. Two prop categorizations based on longevity of use are permanent and temporary; a permanent prop is designed to be in place the duration of the mining and not reusable while a temporary prop would be removed after a period of time and reused.
Temporary supports are used during the excavation of the cavities that are removed and advanced as the excavation work progresses forward down a mine tunnel. These temporary supports typically have hydraulic actuation of a piston to support the heavy loads. The are not yieldable to the ongoing settling process since they are not designed to be in place for an extended period of time. The present invention deals with the problems associated with permanent, primary, yieldable mine posts as well as secondary rehabilitative supports used to shore up areas where primary supports are failing.
The Bureau of Mines has propagated regulations through the Mining Safety and Health Administration (MSHA) that require primary props be in place prior to actual mining. MSHA categorizes permanent props as primary or secondary props. A secondary or rehabilitative prop is used to control portions of the shaft where settling is not properly compensated by the primary supports already in place.
For long term support of a tunnel structure, permanent support members are put into place and must be yieldable to some extent to the settling process described above. Traditionally, this has been accomplished using stacks of wood. Yieldability is measured as a percentage of total support length. For example, a typical eight foot primary wood support can comfortably yield two feet before failure thereby having a 25% yield factor. The greater the yield factor, the percentage yield before support failure, the more versatile the support. The present invention seeks to significantly increase this yield factor over traditional methods while allowing unparalleled versatility in designing primary supports for a specific application.
Wood has various drawbacks including the considerable bulk involved. The more bulk required for the supports, the greater the excavation necessary for a given shaft to allow movement and ventilation. Another drawback to using timber are environmental concerns stemming from deforestation to supply such large quantities of wood as needed in mining sites. This harms the lodge pole pine forests in the western mines and oak forests in the eastern mines.
Many forms of artificial yieldable posts have been developed to varying degrees of cost effectiveness in comparison with the traditional wood. They also have a number of drawbacks in terms of being bulky, expensive, hard to use, etc. These artificial posts may weigh nearly 200 lbs. and cost upwards of $300 a piece while requiring hydraulic power packs or grease guns to install the supports properly. Examples include variations of concrete cribbing and lava rock pillar as well as a number of metal posts found in the prior art.
Another recognized problem in the area of mining is the shifting associated with subterranean settling. As the roof and the floor of a mine shaft settle, there is a tendency for translational (horizontal in all directions) movement of the either the roof or the ceiling or sometimes both. This translational movement causes shifting in support post bases with respect to one another which in turn causes serious structural integrity problems for support posts unable to accommodate these movements.
The present invention addresses these two major problems found in the mining industry simultaneously. Furthermore, the present invention does so in a less expensive, less bulky, and easier to manipulate fashion than has previously been achieved.